DragonFly On-Line Manual Pages
BIO(3) DragonFly Library Functions Manual BIO(3)
BIO -- I/O abstraction
A BIO is an I/O abstraction, it hides many of the underlying I/O details
from an application. If an application uses a BIO for its I/O, it can
transparently handle SSL connections, unencrypted network connections and
There are two types of BIO, a source/sink BIO and a filter BIO.
As its name implies, a source/sink BIO is a source and/or sink of data,
examples include a socket BIO and a file BIO.
A filter BIO takes data from one BIO and passes it through to another, or
to the application. The data may be left unmodified (for example a mes-
sage digest BIO) or translated (for example an encryption BIO). The
effect of a filter BIO may change according to the I/O operation it is
performing: for example an encryption BIO will encrypt data if it is
being written to and decrypt data if it is being read from.
BIOs can be joined together to form a chain (a single BIO is a chain with
one component). A chain normally consist of one source/sink BIO and one
or more filter BIOs. Data read from or written to the first BIO then
traverses the chain to the end (normally a source/sink BIO).
BIO_ctrl(3), BIO_f_base64(3), BIO_f_buffer(3), BIO_f_cipher(3),
BIO_f_md(3), BIO_f_null(3), BIO_f_ssl(3), BIO_find_type(3), BIO_new(3),
BIO_new_bio_pair(3), BIO_push(3), BIO_read(3), BIO_s_accept(3),
BIO_s_bio(3), BIO_s_connect(3), BIO_s_fd(3), BIO_s_file(3), BIO_s_mem(3),
BIO_s_null(3), BIO_s_socket(3), BIO_set_callback(3), BIO_should_retry(3)
DragonFly 4.7 July 17, 2014 DragonFly 4.7
BIO_ctrl(3) OpenSSL BIO_ctrl(3)
BIO_ctrl, BIO_callback_ctrl, BIO_ptr_ctrl, BIO_int_ctrl, BIO_reset,
BIO_seek, BIO_tell, BIO_flush, BIO_eof, BIO_set_close, BIO_get_close,
BIO_pending, BIO_wpending, BIO_ctrl_pending, BIO_ctrl_wpending,
BIO_get_info_callback, BIO_set_info_callback - BIO control operations
long BIO_ctrl(BIO *bp,int cmd,long larg,void *parg);
long BIO_callback_ctrl(BIO *b, int cmd, void (*fp)(struct bio_st *, int, const char *, int, long, long));
char * BIO_ptr_ctrl(BIO *bp,int cmd,long larg);
long BIO_int_ctrl(BIO *bp,int cmd,long larg,int iarg);
int BIO_reset(BIO *b);
int BIO_seek(BIO *b, int ofs);
int BIO_tell(BIO *b);
int BIO_flush(BIO *b);
int BIO_eof(BIO *b);
int BIO_set_close(BIO *b,long flag);
int BIO_get_close(BIO *b);
int BIO_pending(BIO *b);
int BIO_wpending(BIO *b);
size_t BIO_ctrl_pending(BIO *b);
size_t BIO_ctrl_wpending(BIO *b);
int BIO_get_info_callback(BIO *b,bio_info_cb **cbp);
int BIO_set_info_callback(BIO *b,bio_info_cb *cb);
typedef void bio_info_cb(BIO *b, int oper, const char *ptr, int arg1, long arg2, long arg3);
BIO_ctrl(), BIO_callback_ctrl(), BIO_ptr_ctrl() and BIO_int_ctrl() are
BIO "control" operations taking arguments of various types. These
functions are not normally called directly, various macros are used
instead. The standard macros are described below, macros specific to a
particular type of BIO are described in the specific BIOs manual page
as well as any special features of the standard calls.
BIO_reset() typically resets a BIO to some initial state, in the case
of file related BIOs for example it rewinds the file pointer to the
start of the file.
BIO_seek() resets a file related BIO's (that is file descriptor and
FILE BIOs) file position pointer to ofs bytes from start of file.
BIO_tell() returns the current file position of a file related BIO.
BIO_flush() normally writes out any internally buffered data, in some
cases it is used to signal EOF and that no more data will be written.
BIO_eof() returns 1 if the BIO has read EOF, the precise meaning of
"EOF" varies according to the BIO type.
BIO_set_close() sets the BIO b close flag to flag. flag can take the
value BIO_CLOSE or BIO_NOCLOSE. Typically BIO_CLOSE is used in a
source/sink BIO to indicate that the underlying I/O stream should be
closed when the BIO is freed.
BIO_get_close() returns the BIOs close flag.
BIO_pending(), BIO_ctrl_pending(), BIO_wpending() and
BIO_ctrl_wpending() return the number of pending characters in the BIOs
read and write buffers. Not all BIOs support these calls.
BIO_ctrl_pending() and BIO_ctrl_wpending() return a size_t type and are
functions, BIO_pending() and BIO_wpending() are macros which call
BIO_reset() normally returns 1 for success and 0 or -1 for failure.
File BIOs are an exception, they return 0 for success and -1 for
BIO_seek() and BIO_tell() both return the current file position on
success and -1 for failure, except file BIOs which for BIO_seek()
always return 0 for success and -1 for failure.
BIO_flush() returns 1 for success and 0 or -1 for failure.
BIO_eof() returns 1 if EOF has been reached 0 otherwise.
BIO_set_close() always returns 1.
BIO_get_close() returns the close flag value: BIO_CLOSE or BIO_NOCLOSE.
BIO_pending(), BIO_ctrl_pending(), BIO_wpending() and
BIO_ctrl_wpending() return the amount of pending data.
BIO_flush(), because it can write data may return 0 or -1 indicating
that the call should be retried later in a similar manner to
BIO_write(). The BIO_should_retry() call should be used and
appropriate action taken is the call fails.
The return values of BIO_pending() and BIO_wpending() may not reliably
determine the amount of pending data in all cases. For example in the
case of a file BIO some data may be available in the FILE structures
internal buffers but it is not possible to determine this in a portably
way. For other types of BIO they may not be supported.
Filter BIOs if they do not internally handle a particular BIO_ctrl()
operation usually pass the operation to the next BIO in the chain.
This often means there is no need to locate the required BIO for a
particular operation, it can be called on a chain and it will be
automatically passed to the relevant BIO. However this can cause
unexpected results: for example no current filter BIOs implement
BIO_seek(), but this may still succeed if the chain ends in a FILE or
file descriptor BIO.
Source/sink BIOs return an 0 if they do not recognize the BIO_ctrl()
Some of the return values are ambiguous and care should be taken. In
particular a return value of 0 can be returned if an operation is not
supported, if an error occurred, if EOF has not been reached and in the
case of BIO_seek() on a file BIO for a successful operation.
1.0.2h 2016-05-03 BIO_ctrl(3)